From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-9.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id D9D39C3A59E for ; Wed, 21 Aug 2019 16:47:53 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 9A40B2332A for ; Wed, 21 Aug 2019 16:47:53 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 9A40B2332A Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id AD9D66B031E; Wed, 21 Aug 2019 12:47:52 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id A651C6B031F; Wed, 21 Aug 2019 12:47:52 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 904DE6B0320; Wed, 21 Aug 2019 12:47:52 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0002.hostedemail.com [216.40.44.2]) by kanga.kvack.org (Postfix) with ESMTP id 646426B031E for ; Wed, 21 Aug 2019 12:47:52 -0400 (EDT) Received: from smtpin18.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with SMTP id 1023287C5 for ; Wed, 21 Aug 2019 16:47:52 +0000 (UTC) X-FDA: 75847016784.18.fact41_a24c01a9863a X-HE-Tag: fact41_a24c01a9863a X-Filterd-Recvd-Size: 4818 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by imf49.hostedemail.com (Postfix) with ESMTP for ; Wed, 21 Aug 2019 16:47:49 +0000 (UTC) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 9E04B360; Wed, 21 Aug 2019 09:47:48 -0700 (PDT) Received: from arrakis.cambridge.arm.com (usa-sjc-imap-foss1.foss.arm.com [10.121.207.14]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id D35C93F718; Wed, 21 Aug 2019 09:47:46 -0700 (PDT) From: Catalin Marinas To: linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org Cc: Andrew Morton , Vincenzo Frascino , Will Deacon , Andrey Konovalov , Szabolcs Nagy , Kevin Brodsky , Dave P Martin , Dave Hansen , linux-doc@vger.kernel.org, linux-arch@vger.kernel.org, Will Deacon Subject: [PATCH v9 3/3] arm64: Relax Documentation/arm64/tagged-pointers.rst Date: Wed, 21 Aug 2019 17:47:30 +0100 Message-Id: <20190821164730.47450-4-catalin.marinas@arm.com> X-Mailer: git-send-email 2.23.0.rc0 In-Reply-To: <20190821164730.47450-1-catalin.marinas@arm.com> References: <20190821164730.47450-1-catalin.marinas@arm.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: From: Vincenzo Frascino On AArch64 the TCR_EL1.TBI0 bit is set by default, allowing userspace (EL0) to perform memory accesses through 64-bit pointers with a non-zero top byte. However, such pointers were not allowed at the user-kernel syscall ABI boundary. With the Tagged Address ABI patchset, it is now possible to pass tagged pointers to the syscalls. Relax the requirements described in tagged-pointers.rst to be compliant with the behaviours guaranteed by the AArch64 Tagged Address ABI. Cc: Will Deacon Cc: Szabolcs Nagy Cc: Kevin Brodsky Acked-by: Andrey Konovalov Signed-off-by: Vincenzo Frascino Co-developed-by: Catalin Marinas Signed-off-by: Catalin Marinas --- Documentation/arm64/tagged-pointers.rst | 23 ++++++++++++++++------- 1 file changed, 16 insertions(+), 7 deletions(-) diff --git a/Documentation/arm64/tagged-pointers.rst b/Documentation/arm6= 4/tagged-pointers.rst index 2acdec3ebbeb..04f2ba9b779e 100644 --- a/Documentation/arm64/tagged-pointers.rst +++ b/Documentation/arm64/tagged-pointers.rst @@ -20,7 +20,9 @@ Passing tagged addresses to the kernel -------------------------------------- =20 All interpretation of userspace memory addresses by the kernel assumes -an address tag of 0x00. +an address tag of 0x00, unless the application enables the AArch64 +Tagged Address ABI explicitly +(Documentation/arm64/tagged-address-abi.rst). =20 This includes, but is not limited to, addresses found in: =20 @@ -33,13 +35,15 @@ This includes, but is not limited to, addresses found= in: - the frame pointer (x29) and frame records, e.g. when interpreting them to generate a backtrace or call graph. =20 -Using non-zero address tags in any of these locations may result in an -error code being returned, a (fatal) signal being raised, or other modes -of failure. +Using non-zero address tags in any of these locations when the +userspace application did not enable the AArch64 Tagged Address ABI may +result in an error code being returned, a (fatal) signal being raised, +or other modes of failure. =20 -For these reasons, passing non-zero address tags to the kernel via -system calls is forbidden, and using a non-zero address tag for sp is -strongly discouraged. +For these reasons, when the AArch64 Tagged Address ABI is disabled, +passing non-zero address tags to the kernel via system calls is +forbidden, and using a non-zero address tag for sp is strongly +discouraged. =20 Programs maintaining a frame pointer and frame records that use non-zero address tags may suffer impaired or inaccurate debug and profiling @@ -59,6 +63,11 @@ be preserved. The architecture prevents the use of a tagged PC, so the upper byte will be set to a sign-extension of bit 55 on exception return. =20 +This behaviour is maintained when the AArch64 Tagged Address ABI is +enabled. In addition, with the exceptions above, the kernel will +preserve any non-zero tags passed by the user via syscalls and stored in +kernel data structures (e.g. ``set_robust_list()``, ``sigaltstack()``). + =20 Other considerations --------------------